Linked Expanders can allow you to manipulate your expansion string to be replaced by the expander record you are linked to.
For example, in this image:
The Expander - DB_IN_USE_SQLSERVER is linked to DB_IN_USE. Likewise, the expander DB_IN_USE_SQLITE is also linked to DB_IN_USE.
Now in our Stencil Code, the expander we use will be DB_IN_USE.
What then happens is that when code is generated, if the connected database is SQL Server, the expansion string that will be used will be UseSqlServer.